The fluorination reaction, which is the target of the present invention, is classified into a dehydroxyfluorination reaction in which a hydroxyl group is replaced with a fluorine atom. As typical reaction examples relating to the present invention, it is possible to cite 1) a process (Patent Publication 1 and Patent Publication 2) in which a substrate having a hydroxyl group is reacted with a perfluoroalkanesulfonyl fluoride, such as perfluorobutanesulfonyl fluoride, in the presence of a special, strongly basic, organic base, such as DBU (1,8-diazabicyclo[5.4.0]undec-7-ene); 2) a process (Non-patent Publication 1) in which a substrate having a hydroxyl group is reacted with perfluorobutanesulfonyl fluoride in the presence of an organic base, such as triethylamine, and “a salt or complex comprising an organic base and hydrogen fluoride” such as triethylamine tris(hydrogen fluoride) complex; and 3) a process (Patent Publication 3) in which 1-β-D-Arabinofuranosyluracil in 3′,5′-hydroxyl-protected form is reacted with a trifluoromethanesulfonylation agent, such as trifluoromethanesulfonyl fluoride, in the presence of an organic base, such as triethylamine, to convert it to 2′-triflate, followed by a reaction with a fluorination agent comprising “a salt or complex comprising an organic base and hydrogen fluoride” such as triethylamine tris(hydrogen fluoride) complex. Furthermore, there is a report of 4) a process (Non-patent Publication 2) in which a hydroxyl group is converted into a fluorosulfate, followed by replacement with a fluorine anion.    Patent Publication 1: U.S. Pat. No. 5,760,255 specification    Patent Publication 2: U.S. Pat. No. 6,248,889 specification    Patent Publication 3: International Publication 2004/089968 Pamphlet (Japanese Patent Application Publication 2004-323518)    Non-patent Publication 1: Organic Letters (US), 2004, Vol. 6, No. 9, p. 1465-1468    Non-patent Publication 2: Tetrahedron Letters (Great Britain), 1996, Vol. 37, No. 1, p. 17-20